Wireless ranging system

Abstract

A wireless ranging system includes a ranging terminal that transmits a wireless signal including a ranging signal and a communication signal indicating an order of ranging with respect to a first ranging target terminal and a second ranging target terminal, and a first ranging target terminal and a second ranging target terminal that, when receiving the wireless signal, respectively transmits a first response signals and a second response signals consecutively a plurality of times to the ranging terminal. For each time the ranging terminal receives each of the plurality of response signals, the ranging terminal measures an elapsed time from transmission of the wireless signal, and calculates a relative distance between the ranging terminal and the ranging target terminals from a propagation time of each of the plurality of response signals calculated using the elapsed time.

What is claimed is: 
     
       1. A wireless ranging system comprising:
 a ranging terminal to transmit a wireless signal including a ranging signal and a communication signal, the communication signal indicating an order of ranging with respect to a first ranging target terminal and a second ranging target terminal; 
 the first ranging target terminal to, when receiving the wireless signal, transmit a first response signal to the ranging terminal after an elapse of a first offset time based on the order of ranging, and to then transmit the first response signals to the ranging terminal a plurality of times at a first time interval; and 
 the second ranging target terminal to, when receiving the wireless signal, transmit a second response signal to the ranging terminal after an elapse of a second offset time based on the order of ranging, and to then transmit the second response signals to the ranging terminal a plurality of times at a second time interval, wherein 
 for each time the ranging terminal receives each of the plurality of first response signals,
 the ranging terminal measures an elapsed time from transmission of the ranging signal, 
 the ranging terminal calculates a propagation time of each of the plurality of first response signals using:
 a plurality of the elapsed times, each of the plurality of elapsed times is a time until one of the plurality of first response signals is received; 
 the first offset time; and 
 the first time interval, and 
 
 the ranging terminal calculates a relative distance between the ranging terminal and the first ranging target terminal for each of the first response signals using the propagation time of each of the plurality of first response signals, 
 
 for each time the ranging terminal receives each of the plurality of second response signals, 
 the ranging terminal measures an elapsed time from transmission of the ranging signal, 
 the ranging terminal calculates a propagation time of each of the plurality of second response signals using:
 the plurality of the elapsed times, each of the plurality of elapsed times is a time until one of the plurality of second response signals is received; 
 the second offset time; 
 and the second time interval, and 
 the ranging terminal calculates a relative distance between the ranging terminal and the second ranging target terminal for each of the second response signals using the propagation time of each of the plurality of second response signals, and 
 
 the first offset time, the first time interval, the second offset time, and the second time interval are set so that the first response signals and the second response signals are alternately receivable by the ranging terminal one by one such that a first of the first response signals and a first of the second response signals are received before a second of the first response signals is received, the first of the first response signals and the first of the second response signals not overlapping in time. 
 
     
     
       2. The wireless ranging system according to  claim 1 , wherein the communication signal includes a first number of consecutive transmissions that is a number of transmissions of the first response signals to be performed by the first ranging target terminal, and a second number of consecutive transmissions that is a number of transmissions of the second response signals to be consecutively performed by the second ranging target terminal. 
     
     
       3. The wireless ranging system according to  claim 2 , wherein the first ranging target terminal transmits the first response signals in accordance with the number of consecutive transmissions, and the second ranging target terminal transmits the second response signals in accordance with the second number of consecutive transmissions. 
     
     
       4. The wireless ranging system according to  claim 3 , wherein the first ranging target terminal adds, to each of the first response signals, a sequence number indicating a transmission order of the first response signal, and the second ranging target terminal adds, to each of the second response signals, a sequence number indicating a transmission order of the second response signal. 
     
     
       5. The wireless ranging system according to  claim 4 , wherein the ranging terminal detects an error with respect to the first response signals and the second response signals by using the sequence number. 
     
     
       6. The wireless ranging system according to  claim 2 , wherein the first ranging target terminal adds, to each of the first response signals, a sequence number indicating a transmission order of the first response signal, and the second ranging target terminal adds, to each of the second response signals, a sequence number indicating a transmission order of the second response signal. 
     
     
       7. The wireless ranging system according to  claim 6 , wherein the ranging terminal detects an error with respect to the first response signals and the second response signals by using the sequence number. 
     
     
       8. The wireless ranging system according to  claim 1 , wherein the first ranging target terminal adds, to each of the first response signals, a sequence number indicating a transmission order of the first response signal, and the second ranging target terminal adds, to each of the second response signals, a sequence number indicating a transmission order of the second response signal. 
     
     
       9. The wireless ranging system according to  claim 8 , wherein the ranging terminal detects an error with respect to the first response signals and the second response signals by using the sequence number.